Traction control systems for vehicles have utilized many different configurations. In some systems, a hydrostatic drive can utilize hydraulic motors in a series hydraulic circuit. Other systems configure the hydraulic motors in a parallel hydraulic circuit. Parallel hydrostatic drive systems have been further refined by utilizing flow dividers to assist in maintaining the desired traction to each wheel. In some instances, it may be desirable for the difference between the pressure drop across a pair of motors to change based upon operating conditions experienced by the vehicle.
For example, when controlling two motors in series, one of the motors tends to do most or all of the work. This imbalance can be especially true when the motors have case drains, or when the motors have varying speeds (such as, when a vehicle rounds a corner, for example). Also, as parameters change, it would be advantageous for the work done by the different motors to change based on the different conditions (such as, weight distribution or the angle of the machine (e.g., hill climb).
Series and parallel circuits have been used to control two motors. In series motor circuits, the pressure is additive in that the pressure available to the system must be shared by all motors in series. Motors in a series circuit must also be able to accommodate back pressure. Further, in series motor circuits, the flow through all motors is equal. When a vehicle is turning (such as around a corner), the outside wheels spin faster than the inside wheels (which follow a tighter turning radius). Failing to accommodate this can lead to the outside wheels scuffing the surface, or even cavitating the motors.
Parallel motor circuits typically use flow divider(s) to ensure all wheels spin, not just the one with no traction. This configuration can have the same limitation as a series motor circuit: the outside motors require more flow when the vehicle turns. Flow dividers can be a strain on the system (causing pressure drop) in low speed conditions, which can cause operation problems for vehicles operating in a creep mode, such unwanted wheel slip, for example.
It will be appreciated that this background description has been created by the inventor to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.